1. Field of the Invention
The present invention relates generally to a radar guidance system, and, more particularly, to a phase dependent guidance system in which hardware induced phase differences are compensated for without a loss of guidance performance
2. Description of Related Art
A radar guidance and tracking system includes, in its major elements, a high frequency oscillator controlled to produce pulses of relatively high power and relatively short duration. These pulses are applied to a highly directional antenna and the antenna is directed to transmit the pulses towards a target or towards a region in which a target is sought. The receiver, which may be interconnected with the same antenna as the transmitter, is controlled to interconnect the antenna to the receiver during the interval between transmitted power pulses in order to receive reflected energy from a target. Monitoring the antenna direction and timing of reflected pulse returns enables determination of location and range of a target for guidance or tracking purposes.
Target angle (i.e., angle from a reference line such as boresight) in certain guidance systems is determined by channel-to-channel phase differences. However, this requires that channel-to-channel phase matching over the entire range of receiver gain be achieved, otherwise hardware phase differences in the channels can introduce an error which could be prohibitive. Such phase dependence guidance systems produce sum (S) and difference (D) signals from data received at the antenna for each channel. More particularly, the signals for each channel are processed to provide S+jD and S-jD signals where the operator j indicates a 90 phase orientation from the S signals.
One technique that has been used in the past to correct for hardware phase differences is to switch these signals to alternate channels every data collection period. By doing this, the phase difference due to the target angle changes sign resulting in phase differences due to the hardware staying constant. Measured phase differences can then be subtracted for each pair of data collection intervals resulting in substantial nulling of any hardware phase differences. This technique, unfortunately, requires a target angle not varying significantly between data collection periods which is not the usual experience.